A combustible gas or vapor mixture can potentially be present in the confined space of an engine crankcase. Should there be any hotspots in the crank case, at a temperature close to auto ignition of the gas or vapor mixture, an explosion could occur. The crankcase explosion relief valve is a safety device which mitigates the effects of this type of event. The explosion relief valve will open quickly to vent the rapid pressure rise caused by the explosion, and will also prohibit the propagation of any flame to the exterior of the engine's crankcase.
The origin for the development of crankcase explosion relief valves stems from an incident that occurred on the ship “Reina Del Pacifico” on Sep. 11, 1947. An oil mist, which developed within the crankcase of one of the ship's engines, was auto ignited by a hot spot that had generated on one of the internal components of the engine. This resulted in an explosion which claimed the lives of 28 people aboard the “Reina Del Pacifico”. As a result of this incident, and many other similar happenings, a research group known as the British Internal Combustion Engine Relief Association (BICERA) was formed for the purpose of evaluating the causes of such occurrences, and to develop devices and practices for limiting the effects of engine crankcase explosions.
The typical look of an explosion relief valve is a cylindrical device mounted to a crankcase or engine manifold, with the device including a valve plate that releasably covers the opening of the crankcase and a flame arrestor for stifling flames erupting from the crankcase. Occasionally, these devices will be fitted with a directional cover that surrounds the exterior of the valve. The key operations of an explosion relief valve are flame suppression, swift pressure relief, and rapid resealing in the event of an explosion.
Explosion relief valves differ in the flame suppression or arresting method used. Often, the design of the flame arrestor determines the entire form, fit, and pricing of the valve. In the past manufacturers have used oil wetted mesh. In this method, the mesh screen of the valve penetrates inside the crankcase so that it may be wetted with oil during normal operation of the engine. The flame front of the explosion is forced to weave through the narrow gaps of the mesh while being quenched by the oil that is saturated in the mesh screen layers. Other manufacturers use corrugated metal surrounding the outside of the valve plate. When the valve disc opens, the flame front is forced through a series of corrugated metal strips which arrest any flames.
A modern valve developed by Penn Troy Machine Company, Inc. is disclosed in U.S. patent application Ser. No. 13/837,178, filed on Mar. 15, 2013, the disclosure of which is incorporated by reference herein in its entirety. This valve includes a flame arrestor with a single perforated metal screen and a porous metal ribbon with a sinuous shape that is positioned between the metal screen and the center axis of the valve. Similar to the corrugated metal valves discussed above, this valve arrest flames by forcing the flame front caused by an explosion to travel through the perforations of both the porous ribbon and the metal screen, effectively choking out flame propagation while still allowing exhaust gas to be released.
Many current explosion relief valves on the market include a cup shaped valve plate, wherein the flow from the valve inlet is directed at the concave portion of this cup shape. This shape can result in trapping the flow of exhaust gas erupting from the crankcase in the cup shaped region, causing the plate to act as if it were flat, whereby the flow from the inlet largely continues in its direction towards the cap of the valve. This causes the flow of gases exiting the valve to be biased in a direction away from the engine, which is unsafe due to the potential for such gases to reach heat-sensitive or flammable objects. To contain such gases from erupting away from the engine, an external directional cover is often used to redirect the flow of hot exhaust gases to a safer direction during venting.